1. Field of the Invention
The present invention concerns a vibrating gyroscope for accurately measuring angular rotations. Compared with the techniques generally used, this gyroscope proves to be more effective, occupies less space, is simple to embody and is less expensive.
2. Description of the Invention
Vibrating gyroscopes are based on the effect of Coriolis forces due to a rotation imposed on moving masses.
Several embodiments have been previously proposed for embodying a vibrating element sensitive to angular speeds.
The method most frequently used consists of making an annular, hemispherical or cylindrical test body of revolution vibrate perpendicular to its axis of symmetry and of observing the movement of the vibration modes when it is subjected to rotation around said axis.
In the most general case of annular, hemispherical or cylindrical test bodies, the main difficulty derives from the compromise that has to be made between the resonance frequency which increases with the spatial requirement reduction and the time constant which determines the performance and which is improved when the resonance frequency is low. For example, it is virtually impossible to embody a cylindrical test body having a thin wall, a volume smaller than 2 cm3 and a resonance frequency lower than 6 kHz. Now it would be desirable to have small test bodies resonating only between 2 and 3 kHz so as to obtain much improved performances.
The second difficulty originates from the embodiment of the excitation and vibration measuring device, it being understood that the term xe2x80x98excitationxe2x80x99 denotes all the commands required for the proper functioning of these gyroscopes.
Solution put forward to date for creating, detecting and maintaining vibration are basically of the electromagnetic, electrostatic or piezo-electric types.
The electrostatic solutions have advantageous performances when they are used under vacuum so as to reduce losses. Because they require extremely small air gaps, they are difficult to implement inside or outside a hemispherical or cylindrical wall and are thus generally expensive.
The piezo-electric solutions use either a cylinder made fully of a piezo-electric material, or small piezo-electric elements mounted, most frequently by glueing, on a metal cylinder. The solutions have one major drawback when used in gyrometric applications for which they are basically adapted of being unable to adjust the axis of excitation with respect to the vibrating body which generally has one overriding direction for which performances are optimum.
For various reasons and in particular for reasons of cross talk, the means for detecting and exciting the vibrations of certain embodiments, are heterogeneous and are spaced as far a s possible from one another.
For example, the U.S. Pat. No. 4,793,195 describes a gyrometer with a vibrating cylinder provided with electrostatic detection and magnetically excited at a frequency half its vibration frequency so as to reduce these effects.
The French patent application 97/12129 describes a gyrometer with multiplexed magnetic detection and excitation which clearly resolves the difficulty of crosstalk between excitation and detection but whose performances are limited by Vie resonance frequency which remains high.
The present invention brings about an improvement which, in a given spatial requirement, makes it possible to choose the resonance frequency and via its principle offers new possibilities for simply and cheaply embodying electromagnetic or electrostatic detection and excitation means.
So as to reach this result, the thin-walled test body of revolution comprises at its periphery evenly distributed masses separated by intervals which increase the moving mass when said test body is excited on vibration Openings can be fitted in the thin wall of the cylinder and not covered by the masses so as to adjust the stiffness of the end of these masses and thus the resonance frequency. This makes it possible to significantly reduce the resonance frequency of said test body and thus increase performances.
By acting on the shape of the openings, it is possible to favour certain types of movements of additional masses and thus embodying inexpensive flat electrostatic or magnetic detection/excitation units able to be placed at the right of a flat open extremity of the test body and thus extremely easy to adjust.
Thus, the invention concerns a vibrating gyroscope of the type comprising:
a thin and vibrating element and approximately generated by rotation,
excitation means for generating vibrations at least one point of the vibrating element so as to make appear on said vibrating element vibration modes able to be modified under the effect of an angular speed of rotation, and
means for detecting said vibrations and arranged so as to be able to detect said vibration modes,
characterised in that the vibrating element approximately generated by rotation at receives at least three and preferably eight masses forming vibrating masses and preferably constituted by excessive thicknesses of the vibrating element itself.